Palladium-Catalysed Intramolecular Cyclisation of Olefinic Propargylic Carbonates and Application to the Diastereoselective Synthesis of Enantiomerically pure (-)-α-Thujone

Abstract

Intramolecular [Pd2(dba)3]/tri(2-furyl)phosphine-catalysed (dba = dibenzylideneacetone, PhCH= CHCOCH=CHPh) cyclisations of olefinic propargylic carbonates I provided alk-1-enyl-(3-aza)bicyclo[3.1.0]-hexanes VIII in good yields. A palladium cascade sequence I → II → III → IV → VII → VIII is proposed. Furthermore, chiral propargylic carbonates such as 23, 24 and 25 allowed diastereoselective formation of bicyclo[3.1.0]hexanes 29, 30 and 31, respectively. The first diastereoselective synthesis of the monoterpene, (-)-α-thujone 40 illustrates the potential of the method.